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248
8.17
PREFETCH command (34h)
The PREFETCH command (Table 181) requests that the drive read and transfer the specified logical blocks to
the drive's cache memory. No data shall be transferred to the initiator.
Table 181:
PREFETCH command (34h)
Bit
7
Byte
0
OPERATION CODE (34h)
1
LOGICAL UNIT NUMBER
2
(MSB)
3
4
5
6
Reserved
7
(MSB)
8
9
CONTROL [4]
[1]
An Immediate (IMMED) bit of one indicates that status shall be returned as soon as the command
descriptor block has been validated. An Immed bit of zero indicates that status shall be returned after the
operation is complete.
[2]
A Relative Address (RELADR) bit of one indicates that the LOGICAL BLOCK ADDRESS field is a two's
complement displacement. This negative or positive displacement is to be added to the LOGICAL BLOCK
ADDRESS last accessed on the logical unit to form the LOGICAL BLOCK ADDRESS for this command.
This feature is only available when linking commands. The feature requires that a previous command in
the linked group have accessed a block of data on the logical unit.
A RELADR bit of zero indicates that the LOGICAL BLOCK ADDRESS field specifies the first logical block
of the range of logical blocks to be operated on by this command.
[3]
The TRANSFER LENGTH field specifies the number of contiguous logical blocks of data that shall be
transferred to the drive's cache memory. A TRANSFER LENGTH value of zero indicates that the contigu-
ous logical blocks up to and including the last logical block of the logical unit shall be transferred to the
drive's cache memory. Any other value indicates the number of logical blocks that shall be transferred.
The drive may elect to not transfer logical blocks that already are contained in the cache memory.
If the Immed bit is zero and the specified logical blocks were successfully transferred to the cache mem-
ory, the drive shall return CONDITION MET status. If the Link bit (see Table 61, "CONTROL field," in Sec-
tion 7.2.1) is one, the drive shall return INTERMEDIATE–CONDITION MET status.
If IMMED is one, and the unlocked cache memory has sufficient capacity to accept all of the specified log-
ical blocks, the drive shall return CONDITION MET status. If the LINK bit (see Table 61, "CONTROL field,"
in Section 7.2.1) is one, the drive shall return INTERMEDIATE–CONDITION MET status.
If IMMED is one, and the unlocked cache memory does not have sufficient capacity to accept all of the
specified logical blocks, the drive shall return GOOD status. The drive shall transfer to cache memory as
many logical blocks as will fit. If the LINK bit (see Table 61, "CONTROL field," in Section 7.2.1) is one, the
drive shall return INTERMEDIATE status.
[4]
See Table 61, "CONTROL field," in Section 7.2.1.
8.18
PRVENT/ALLOW MEDIUM REMOVAL command (1Eh)
Not implemented by the drive. If received, the drive terminates with CHECK CONDITION status and sets an
ILLEGAL REQUEST sense key.
6
5
LOGICL BLOCK ADDRESS [2]
TRANSFER LENGTH [3]
SCSI Interface Product Manual, Rev. B
4
3
Reserved
2
1
IMMED [1]
RELADR [2]
(LSB)
(LSB)
0
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